Mojave 10.14.1 External Monitor Not Working

I have the same issue. Just bought a Dell P2719H, and I have a 2018 MacBook Air running on Mojave.

Tried every single fix I could google but no luck, not a blink from the screen.

Does Apple care about any of this?

I had this exact issue on my MacBook Air (2015). I wrote a quick blog on it which I hope you find helpful.

http://www.wonkydata.com/post/180498917779/how-to-actually-connect-two-monitors-to-a-macbook

My solution works for TWO monitors.

Now I've upgraded to a Macbook Pro, and I have a third monitor - not working.

• Three monitors not working. Only two at a time are recognized.
• I can switch out which are plugged into my USB-c ports, and it doesn't matter which are connected, only the first two plugged in (in sequence) are recognized. I can change the sequence, and it only changes which two monitors are recognized and function. One is always left in an unrecognized state.
• I've tried "detect displays" (does not detect a third, in any order).
• I've rebooted x *
• I've updated the DisplayLink drivers.
• I've made sure that the drivers are enabled in "security & privacy" settings.
• I've switched out all of my adaptors (CableCreation USB-C to HDMI). All three of my monitors are Samsungs: two S27D360's, one C27F390

My computer: MacBook Pro (13-inch, 2017, Four Thunderbolt 3 Ports); 16GB.

Mojave: 10.14.3

@apple Help. This is ridiculous.

Mojave 10.14.1 refuses to recognise my LG external monitor since I connected it to my new Android TV box 🙂

Pretty weird issue. All other HDMI monitors are working and the monitor is working with other HDMI sources.

Tried about everything I could find. NVRAM/SMC reset, delete windowserver preference files aso.

I think the only solution would be to reinstall the display driver, but there is no such option on macOS.

Will try to reinstall it from a TimeMachine backup, see if that fixes it.

I have similar issue with my Macbook Pro. My external monitor is working but it turns black randomly. It turns black for a few seconds than it works again, then black again etc. ect. Sometimes no issues other times constantly 'like today'.

Sometimes it helps when I switch ports. I use the thunderbolt port to hdmi. It's like when the cable is broken or the thunderbolt port is not good, but That is not the probleem because With High sierra I never had any issues. It started the first day after upgrading to Mojave.

I have tried so many things but for as now nothing seems to work.

Any Help?

I have this same exact problem. The monitor works with every other device (e.g. ios device with adapter) and the macbook pro works with the same adapter on any other display. So it seems that in some way the display got "blacklisted" (obviously it did not but every piece is working but the whole system does not work).

Apple is not here. This is a user to user forum.

We don't know which fixes you "googled", so in order to try to help we need to know more - you did not even say which adapter you used to connect your mac to the display.

There have been issues with connecting to displays, but they are not all the same. In some cases, it is related to docks that rely on "displaylink" software to work, in others it is not - as when connected directly via HDMI. The latter are the most puzzling.

It makes it harder yet because while certainly some people have this problem, most people don't. I have used my 2014 MBP with over a dozen different displays, with connections using direct HDMI, miniDP->HDMI, miniDP->VGA, as well as direct Thunderbolt (which I am using as I write this with an older iMac in target display mode). All of them have worked.

Fair enough, here is the missing info:

I am using a 2017 MacBook Air, connecting to a Dell P2719H display I just bought. Running on Mojave.

To connect I use a MiniDP => HDMI adaptor and and HDMI cable to the computer.

I have tried the same connection on a similar MacBook Air (2016) and have tried to connect to an HP EliteDisplay E240.

Fixes: I have tried resetting NVRAM and SMC, re-installing Mojave, updating Mojave to latest version 10.14.3, I have even tried to downgrade to High Sierra (but have failed to do it, for some reason it doesn't allow me to erase the HD).

I am getting a MiniDP to DP adapter later today, which I will then try with a DP cable that came with the screen. Otherwise I am out of options.

I have similar issue - built-in HMDI port doesn't work when booted with macOS 10.14.3, but worked perfectly before upgrade (latest macOS 10.13).

MacBook Pro Retina 15" mid2014 (MacBookPro11,3)

Seki SE39UY04

I switched to hdmi port. My problem is with both the 2 tunderbolt ports to hdmi. Since i switched to the HDMI port the problem is solved. But nevertheless with tunderbolt to hdmi still noth working proper.

I don’t quite understand. You jumped through hoops and were able to connect two displays to an older MacBook Air - a configuration that worked even though it was unsupported. That is great.

What has that got to do with the newer MacBook Pro? It does support two external displays, but now you want three?

The only way for me to use the dell display was to use it over display port. Since we had lots of them in the office, most (but not all) of them is having troubles via DVI. With display ports seems to work consistently. Hope it helps!

I have this issue as well. Works when I reset the NVRAM. Seems to stop working when the mac goes to sleep. Need to reset NVRAM everytime I want to use the external monitor.

I'm having a similar problem with a late 2013 iMac 27". My external display is showing "no signal" 😟.

Hopefully you found a solution. I had the same issue. My solution was to go from the old VGA on monitor to VGA/Thunderbolt 3 adaptor on 2018 iMac which worked.